Frequency-tunable multielement antenna structure

ABSTRACT

An antenna structure is provided having a plurality of elongated antenna units that are supported in mechanically coupled, longitudinally extending, side-by-side relationship but are relatively flexible to a spaced relationship for obtaining resonance at a predetermined frequency. Each antenna unit includes one or more electrically conductive elements with the elements of all units electrically interconnected at one end and structurally supported and protectively encased in a dielectric material comprising a fiber-glass-reinforced synthetic resin matrix.

[ Feb. 29, 1972 United States Patent Francis et al.

0 0 9 M 4 3 S n N m m m T. m A m m m L m P n P u m m I- mm 0 m mm an m 8 4 6 A w EE LT BN AA T N JE Y M E ER N L U EET U C Q U a F M S M 5 Primary Examiner-Herman Karl Saalbach Assistant ExaminerMarvin Nussbaum Attorney-Mahoney, Miller & Stebens [72] Inventors: Richard .I. Francis; Clara A. Francis, both of H855 Broad St., Pataskala, Ohio 43062 [22] Filed: July 22, 1974) ABSTRACT An antenna structure is provided having a plurality of elongated antenna units that are supported in mechanically coupled, longitudinally extending, side-by-side relationship but 2: Appl. No.: 57,285

[52] US. Cl...............................343/723, 343/749, 343/826,

343/895 .l'lolq 1/40, HOlq 9/46, HOlq 21/00 are relatively flexible to a spaced relationship for obtaining resonance at a predetermined frequency. Each antenna unit [51] Int. [58] Field of Search 895-897, 343/860-862, 747, 749, 826

includes one or more electrically conductive elements with the elements of all units electrically interconnected at one end and structurally supported and protectively encased in a [56] References Cited UNITED STATES PATENTS dielectric material comprising a fiber-glass-reinforced synthetic resin matrix.

.343/826 11 Claims, 15 Drawing Figures mmuflhhm iak 3 a?! PAIENIEHFEB 29 IBIZ SHEET 1 OF 4 mmzoqmmm FREQUENCY INVENTORS. RICHARD J. FRANCIS 8- 'BYCLARA A. FRANCIS MAHONEY. MILLER & STEB ATTORNEYS PATENTEDFEBZQ I972 3,646. 563

sum 2 or 4 INVENTORS RICHARD J. FRANCIS 8. BY CLARA A. FRANCIS MAHONEY. MILLER 8. STEB S ATTORNEYS PAIENTEDFEBZS I972 3. 646, 563

snm 3 or 4 I N VEN TORS RICHARD J. FRANCIS & BY CLARA A. FRANCIS MAHONEY. MILLER & STEBENS ATTORNEYS FREQUENCY-TUNABLE MULTIELEMENT ANTENNA STRUCTURE BACKGROUND OF THE INVENTION The antenna structure of this invention is primarily adapted to mobile installations for both transmitting and receiving functions such as citizens-band operations in connection with automotive vehicles although the antenna structure is adaptable to other frequency band allocations. For installations of this type, the antennas of prior art constructions generally comprise a single electrically conductive element effective as both a receiver and radiator of electromagnetic wave energy in the selected radiofrequency spectrum and is of a physical construction to accommodate the mechanical forces that may be applied as a consequence of vehicular movement. Antennas of prior art construction for mobile installations are most commonly an electrical quarter wave in length and metallic ranging in length from about 9 feet for 27 megahertz to about 6 inches for 470 megahertz. These antennas are usually vertically mounted and supported only at the bottom and are endfed. Vertical quarter-wave antennas of a length in the range of 9 feet are physically unwieldly; however, an antenna in the 1-500 megahertz range may be physically shortened by adding inductance in series. Conversely, the physical length, commonly called aperture, may be increased by adding capacitance in series.

A transceiver is connected with the antenna through a coaxial cable and the most commonly used coaxial cable has a characteristic impedance of 52 ohms. The output stage of the transceiver is adjustable to 52 ohms. However, the terminal impedance of an end-fed quarter wave is well below 52 ohms, perhaps as low as ohms. Maximum power transmission results when the terminal impedance of the end-fed quarterwave antenna matches the impedance of the coaxial transmission line. With the single element antennas of prior art the impedance mismatch is great enough to seriously impede the efficiency of power transferral. Some installations are operated inefficiently with this mismatch, while other installations rely on complex impedance matching networks to correct this mismatch.

The antenna is usually mounted in an upright position and located at any one of several physical locations on a vehicle body. The vehicle body, when fabricated from an electrically conductive metal as is the usual case, acts as a ground plane for the antenna and, since the body surface is irregular, mounting of an antenna at the difl'erent locations such as bumper, fender, cowl or roof will have a substantial effect on the resonant frequency of an antenna structure. An antenna is normally cut or formed to a specific length for a particular operating frequency and when mounted on the vehicle will require adjustment of some type to obtain resonance at the particular frequency with the adjustment depending on the antenna mounting location. An antenna which is resonant at one location on a vehicle body may not be resonant or work well at another location.

BRIEF DESCRIPTION OF THE INVENTION The antenna structure of this invention comprises a plurality of units that are mechanically and electrically interconnected or intercoupled to provide optimum impedance matching and obtain resonance at the desired operating frequency for the specific location of the antenna on the vehicle body. Each antenna unit includes one or more electrically conductive elements of an appropriate length for the selected nominal operating frequency with these elements being structurally supported by a dielectric material such as a synthetic resin matrix. The antenna units which are elongated structures are mechanically intercoupled at one end to permit the remainder or free portions of the units to be relatively flexed to obtain a spacing that results in resonance of the antenna structure at a specified frequency. Mechanical means is pro vided to obtain and maintain the relative spacing of the units with the units being flexed into relatively divergent relationship from the interconnected ends that form a tenninal or mounting end for the antenna structure. The marginal end portions of the units adjacent the interconnected ends are relatively tangential and remain so disposed when the antenna units are flexed to the desired position.

FIG. 1 is a fragmentary elevational view, partly in section, of an antenna structure embodying this invention.

FIG. 2 is a transverse sectional view taken along line 2-2 of FIG. 1.

FIG. 3 is a transverse sectional view taken along line 33 of FIG. 1.

FIG. 4 is an elevational view of a modified fonn of the antenna structure.

FIG. 5 is a transverse sectional view taken along line 5-5 of FIG. 4.

FIG. 6 is an elevational view of a further modified from of the antenna structure.

FIG. 7 is a transverse sectional view taken along line 7-7 of FIG. 6.

FIG. 8 is a medial longitudinal sectional view of a further modified form of antenna structure.

FIG. 9 is a transverse sectional view taken along line 99 of FIG. 8.

FIG. 10 is a fragmentary longitudinal sectional view of an antenna unit with a modified antenna element configuration.

FIG. 11 is a transverse sectional view taken along line 11- ll of FIG. 10.

FIG. 12 is a graphic representation of a response-frequency characteristic for an antenna structure having a plurality of dissimilar diameter elements.

FIG. 13 is a medial longitudinal sectional view of a portion of a further modified form of antenna structure.

FIG. 14 is a transverse sectional view taken along line 14-14 of FIG. 13.

FIG. 15 is a medical longitudinal sectional view of a portion of a further modified form of antenna structure.

DETAILED DESCRIPTION OF THE INVENTION Having reference to FIGS. 1-3 of the drawings, an antenna structure embodying this invention is illustrated in detail. This antenna structure comprises a pair of similarly configured antenna units 10 and 11 each of which includes a respective electrically conductive element or conductor, 12 and 13, encased in a structurally supporting body 14. The two electrically conductive elements 12 and 13 in each unit are effective, at the design radiofrequencies, for radiation or reception of electromagnetic wave energy.

The conductive elements 12 and 13 are preferably formed from elongated segments of small diameter copper wire of adequate size to handle the power up to watts found in mobile transceiver. While No. 24 A. W. G. will handle this power, the elements will not be structurally self-supporting. An antenna structure of this invention is particularly adapted to utilization with mobile vehicular installations and these installations are normally operated in the 1-500 megahertz frequency spectrum where a quarter-wave antenna will have a substantial length. In the case of equipment operating in the citizens-band frequency spectrum at the nominal operating frequency of 27 megahertz, a quarter-wave length will be or the order of 8 feet and it will be readily seen that this length precludes reliance on the structural strength of the conductive elements for structural integrity of the antenna structure. Accordingly, a structurally supporting body 14 of circular cross section is provided to adequately maintain the several conductive elements in a specific configuration and permit vertical mounting of the antenna on a vehicle. In the illustrated embodiment which is designed for operation at a nominal operating frequency of MHz., the length and diameter of each unit 10 and 11 is of the order of 15 inches and three-sixteenth inch, respectively. This body 14 in accordance with this invention is formed from a dielectric material which is a synthetic resin matrix having the necessary mechanical characteristics as to flexural strength and modulus for the specific design application to withstand the static and dynamic loads that may be encountered in vehicular installations and maintain the specific element configuration while permitting flexing of the antenna units and 11. Preferably, the synthetic resin matrix, which may comprise a thermosetting polyester or epoxy, also includes strands of fiber glass distributed throughout the body to enhance the mechanical properties of the antenna structure. These strands of fiber glass 15 are preferably oriented longitudinally of the antenna units. While each unit 10 and 11 of the illustrated unit is shown as being of a cylindrical shape, it will be understood that the body 14 may be tapered with a relatively reduced diameter at the outer or free end in the case of relatively long antenna structure and also that the diameter may be other than three-sixteenth inch, such as with the range of one-eighth to one-half inch, as determined most advantageous for a specific structure when considering appropriate construction factors, length, for example.

Interconnection of the antenna with a radio installation, as well as mechanical support or mounting of the antenna, is accomplished by means of a mounting ferrule 16. The ferrule 16 is formed from an electrically conductive metal with a central socket 17 in which the ends of the two antenna units 10 and 11 may be inserted and secured as by a suitable adhesive or bonding material 18 that may also fill voids in the ferrule socket 17 and is not electrically conductive. The terminal ends of the conductive elements 12 and 13 of each unit project from the resin matrix body 14 and are electrically interconnected and extend into an aperture 19 formed in the ferrule 16 and are electrically connected to the ferrule as by a solder connection 20. The ferrule 16 is also provided with a threaded portion 21 for mechanical interengagement with a mounting socket (not shown).

Optimum tuning of the antenna for operation at the desired frequency is accomplished through flexing of the two units 10 and 11 to a desired spaced relationship as is best shown in FIG. 1. Flexing of the units to the desired spaced relationship and maintenance in this position is readily accomplished by means such as a spacing element or spreader bar 25. This bar is formed from a sheet of rigid dielectric material having V- shaped notches 26 cut in the opposed ends and of a dimension to accommodate the diameter as the antenna units 10 and 11. Positioning of the bar 25 between the units 10 and l 1 adjacent the outer or free ends with the units 10 and 11 in the respective notch 26 and sliding the bar downwardly toward the ferrule 16 flexes and spaces the units in a relatively divergent manner with the spacing or divergence being determined by the specific installation and is most accurately accomplished with the antenna mounted on the vehicle. After the optimum spacing is obtained, the spacer bar 25 may be rigidly secured to the antenna units by wrapping the antenna units and bar with a self-adhesive tape 27 that is formed from a dielectric material. This tape 27 is shown in FIGS. 1 and 3 as first being wrapped circumferentially around the assembled units and bar and secondly being wrapped around the central portion of the bar. In the case of the specific embodiment illustrated in FIGS. 1-3, designed for a nominal operating frequency of 150 MHz. and having a length of the order of 15 inches, the units 10 and 11 may be readily flexed to a maximum extent by means of a spreader bar 25 having a length of 1 inch and positioned at about 10 inches from the ferrule 16. This changes the nominal operating frequency of 150 MHZ. with the antenna units 10 and 1 l substantially parallel to a nominal operating frequency of the order of I35 MHz. with the antenna units flexed to the indicated maximum thus representing a resonant frequency range of the order of 10 percent that is easily achieved. This numerical example is merely presented for illustrative purpose and is not limitative since it is readily apparent that other constructions and dimensional factors will result in alteration of these characteristics. It will also be noted that the antenna units 10 and 11 are tangentially disposed at their interconnected ends at the ferrule 16 resulting in coextensive portions of the conductive elements 12 and 13 being spaced parallel and then gradually diverging without any sharp angle of inter section thereby aiding in achieving optimum performance.

Appropriate spacing of the antenna units may also be achieved by the technique shown in FIG. 4. With this technique, the outermost ends of the two antenna units 10a and 11a are mechanically secured together as by a clip-form fastening device 28, but the conductive elements are not electrically interconnected at this end. A spacing element or bar' 29 of an appropriate length and end notches 30 (see FIG. 5) is inserted between the antenna units 10a and 11a and may be moved longitudinally of the units to obtain the optimum spac-- ing. After properly locating the spacer bar 29, the bar may be rigidly secured in position by wrapping the antenna units 1th: and 11a with an adhesive tape 31 as described in conjunction with the previous embodiment. The fastening device 28 and the spacer bar 29 are both formed from a dielectric material having the necessary structural rigidity.

The previously described embodiments include two antenna units; however, the advantageous spacing adjustment may also be utilized in connection with embodiments having three or more antenna units such as the three-unit structure shown in FIGS. 6 and 7. Each ofthe three units 35, 36 and 37 may be of the same construction as previously described with the ends of each unit mechanically secured in a ferrule 38. A spacer bar 39 comprising a triangularly shaped sheet of rigid dielectric material having three notches 40 formed therein is positioned at an appropriate point between the antenna units 35, 36 and 37 and is secured in position by wrapping with tape 41. Each unit includes an electrically conductive element 35 a, 364 and 37a with all three elements electrically interconnected and connected to the ferrule 38.

The previously described and illustrated embodiments of the antenna structure are constructed with only one electrically conductive element in each antenna unit. Further modified embodiments may be constructed with a plurality of electrically conductive elements in each antenna unit as it shown in FIGS. 8-11. Referring to FIGS. 8 and 9, an antenna structure is shown having two antenna units 45 and 46 that include three respective conductive elements 47, 48, 49 and 50, 51, 52. The several elements in each unit are electrically insulated from each other throughout their length but are electrically interconnected to each other at the terminal end and to a ferrule 53. Electrical insulation of the elements may be accomplished by coating one or all of the elements with a suitable dielectric material such as a varnish forming a respective sheath 17a, 48a, 49a and 50a, 51a, 52a around the elements of the spacing of the elements with the dielectric matrix 54 forming the supporting body does not provide the necessary insulation. Although the three elements in each antenna unit are shown arranged in a triangular configuration, it will be understood that other configurations may be utilized. Optimum impedance matching of the antenna is enhanced through selection of conductive elements of appropriate cross-sectional area and through relative spacing of these elements in the respective units. As an example, the pairs of elements 47', 50; 48, 51; and 49, 52 may be No. 24, 26 and 28 A. W. 6., respectively, with the elements being relatively spaced by th dielectric sheaths.

Resonant length of a conductor variesslightly as the diameter changes. Using conductors or elements of different diameters broadens the effective resonant range of an antenna structure as the peaks of response for each element are relatively offset with respect to frequency. This is graphically illustrated in FIG. 12 for two dissimilar diameter elements M and N.

The electrically conductive elements in the respective embodiments of the antenna units may be helically wound rather than linearly configured as previously described. This helical configuration is shown in FIGS. 10 and 11 with respect to a fragmentary portion of a single antenna unit 55 having three conductive elements 56, 57 and 58. These elements are each electrically insulated from the others throughout their length by respective vamish-type coatings or dielectric sheaths 56a, 57a and 580. This antenna unit 55 may be readily fabricated by winding the conductive elements 56, 57 and 58 on a preformed core 59 which is formed from a dielectric material and is thus encased in an outer sheath 60 of the same material.

The fabrication technique is such that the core 59 and outer sheath 60 form a unitary structure. Appropriate dimensioning of the core diameter and spacing of the turns of the helix, ssinch diameter with l/ 16-inch longitudinal turn spacing, for example, provides the desired impedance characteristic for an antenna structure of appropriate length for a designed nominal operating frequency if 27 MHZ. The three elements 56, S7 and 58 may also be of dissimilar diameter to obtain a desired antenna characteristic.

FIGS. 13 and 14 illustrate a base portion of an antenna structure having two antenna units 65, 66 secured by a suitable adhesive 67 in an elongated tube 69 secured in a ferrule 68 and including an inductive coil 70. The tube 69 is formed from a dielectric material similar to that of the antenna units 65 and 66. The two units 65, 66 are each formed as described in detail with respect to the embodiment shown in FIGS. 1-3 and include the respective single conductive elements 71 and 72 that extent longitudinally through the unit and termed a linear configuration. These conductive elements 71 and 72 are electrically interconnected within the opposite end of the coil electrically connected to the ferrule 68 as by a solder connection 73. The coil 70 is wound on the tube 69 at a point above the ferrule 68 with the terminal ends of the antenna units 65 and 66 outward of the coil and the coil is dimensioned to obtain impedance matching and resonance at the desired frequency in conjunction with selective spacing of the antenna units as previously described. Aperture 74 and 75 are formed in the wall of the tube 69 to facilitate connection of the coil 70. A tubular sheath 76 also of dielectric material is also provided for protection of the coil. This sheath is structurally rigid and is adhesively secured to the outer surface of the ferrule 68 and may also be sealed to the antenna units 65 and 66 at the outer end.

For 27 MHz, a quarter-wave length in air in 9 feet but a quarter-wave fiber glass antenna will only be about 8 feet long, largely because the fiber glass body dielectrically compresses resonance. However, 8 feet is too long for many installations and it is the function of the inductive coil 70 to act as or form part of the antenna to reduce its length. An inductive coil or loading coil can reduce the length to about 1 foot, but, generally, the length can only be reduced to a range of 2 to 4 feet so that the antenna structure will still have an effective aperture area.

The antenna structure shown in FIG. is a modification of that shown in FIGS. 13 and 14 with this structure also comprising two antenna units 80 and 81 secured by a suitable adhesive 82 in a tube 83 which is secured in a ferrule 84 and includes an inductive coil 85. The two units 80 and 81 are formed as previously described and include respective single conductive elements 86 and 87 extending longitudinally through the unit. Both conductive elements 86 and 87 are electrically interconnected with the tube 83 and in series with an end of the coil 85. The opposite end of the coil 85 is electrically connected to the ferrule 84 which is fabricated from an electrically conductive material and ferrule is formed with a coaxial conductor 88 extending through an aperture 89 in the ferrule base and supported by dielectric spacers 90. This conductor 89 is connected to the coil 85 by a lead 91 extending through the aperture 92 in the tube wall to tap point which may be the fourth turn of a -tum coil to provide a better impedance match for connection with a coaxial cable. A protective tubular sheath 93 may also be provided.

it will be readily apparent that a novel antenna structure is provided having improved characteristics with a capability of being tuned for optimum operation at a particular desired mounting location on a vehicle. Fiber glass construction provides structural rigidity and protection for relatively small diameter conductive elements in a multiunit antenna structure while permitting flexing of the antenna units for tuning purposes.

Havin thus described this invention, what is claimed is: 1. A requency-tumable antenna structure compnsrng at least two elongated antenna units disposed in longitudinally extending relationship and mechanically interconnected at one end forming a terminal end of the antenna structure with the marginal end portions of each unit adjacent the interconnected ends being tangential relative to each other, each said antenna unit including an elongated electrical conductor and a body structure formed from a dielectric material in which said conductor is embedded for support thereof with said conductors being electrically interconnected at the terminal end, said dielectric material having a relatively low loss characteristic as to electromagnetic wave energy and a physical strength characteristic to maintain the physical configuration of said conductors and assure structural integrity of the antenna structure while permitting flexing of said units, and a spacing element positionable between said antenna units in mechanical interengagement therewith at a point intermediate the interconnected marginal end portions and the opposite ends for flexing said units into relatively divergent relationship from the tangentially disposed marginal end portions for resonance at a selected frequency and maintaining said units in such flexed relationship.

2. An antenna structure according to claim 1 having an inductive coil serially connected with said electrical conductors at the terminal end.

3. An antenna structure according to claim 2 having a coil form supporting said coil thereon in axially aligned relationship to said antenna units.

4. An antenna structure according to claim 2 wherein said coil comprises a plurality of turns with an intermediate one of said turns having a tap point forming the antenna feed point for optimum impedance matching with one end of said coil connectable with an electrical ground.

5. An antenna structure according to claim 1 having at least three antenna units disposed in equally spaced relationship with said spacing element interengageable with each antenna unit for flexing said units and maintaining said units flexed in the equally spaced relationship.

6. An antenna structure according to claim 1 wherein said spacing element comprises an elongated bar of dielectric material with antenna unit-receiving notches formed therein in relatively spaced relationship.

7. An antenna structure according to claim 1 having fastening means of dielectric material mechanically interengaged with said antenna units at the marginal end portions.

8. An antenna structure according to claim 1 wherein each antenna unit includes a plurality of electrical conductors extending throughout the length thereof and electrically insulated from each other throughout their length but electrically interconnected at the terminal end.

9. An antenna structure according to claim 8 wherein said electrical conductors are longitudinally extending, linear elements.

10. An antenna structure according to claim 8 wherein said electrical conductors are formed in a longitudinally extending helix.

11. An antenna structure according to claim 8 wherein said electrical conductors in each antenna unit are of dissimilar diameters.

it i

UNITED STATES PATENT,- OFFICE CERTIFICATE OF CORRECTION Patent No. 3,6464563 Dated. February 29 1972 Inventor(s) Richard J. Francis; Clara A. I Francis It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

Column 6. line 52, after "the", insert end opposite said terminal end and preventing separation of the--.

Signed and sealed this 25th day of July 1972.

(SEAL) A ttest:

EDWARD M.FLETCHER JR. ROBERT GOTTS CHALK Attesting Officer Commissioner of.Patents FQRM -1 uscoMM-oc scan-Pea U. GOVINIINT PIIITI IG O'PICI I... o-QCI-i 

1. A frequency-turnable antenna structure comprising at least two elongated antenna units disposed in longitudinally extending relationship and mechanically interconnected at one end forming a terminal end of the antenna structure with the marginal end portions of each unit adjacent the interconnected ends being tangential relative to each other, each said antenna unit including an elongated electrical conductor and a body structure formed from a dielectric material in which said conductor is embedded for support thereof with said conductors being electrically interconnected at the terminal end, said dielectric material having a relatively low loss characteristic as to electromagnetic wave energy and a physical strength characteristic to maintain the physical configuration of said conductors and assure structural integrity of the antenna structure while permitting flexing of said units, and a spacing element positionable between said antenna units in mechanical interengagement therewith at a point intermediate the interconnected marginal end portions and the opposite ends for flexing said units into relatively divergent relationship from the tangentially disposed marginal end portions for resonance at a selected frequency and maintaining said units in such flexed relationship.
 2. An antenna structure according to claim 1 having an inductive coil serially connected with said electrical conductors at the terminal end.
 3. An antenna structure according to claim 2 having a coil form supporting said coil thereon in axially aligned relationship to said antenna units.
 4. An antenna structure according to claim 2 wherein said coil comprises a plurality of turns with an intermediate one of said turns having a tap point forming the antenna feed point for optimum impedance matching with one end of said coil connectable with an electrical ground.
 5. An antenna structure according to claim 1 having at least three antenna units disposed in equally spaced relationship with said spacing element interengageable with each antenna unit for flexing said units and maintaining said units flexed in the equally spaced relationship.
 6. An antenna structure according to claim 1 wherein said spacing element comprises an elongated bar of dielectric material with antenna unit-receiving notches formed therein in relatively spaced relationship.
 7. An antenna structure according to claim 1 having fastening means of dielectric material mechanically interengaged with said antenna units at the marginal end portions.
 8. An antenna structure according to claim 1 wherein each antenna unit includes a plurality of electrical conductors extending throughout the length thereof and electrically insulated from each other throughout their length but electrically interconnected at the terminal end.
 9. An antenna structure according to claim 8 wherein said electrical conductors are longitudinally extending, linear elements.
 10. An antenna structure according to claim 8 wherein said electrical conductors are formed in a longitudinally extending helix.
 11. An antenna structure according to claim 8 wherein said electrical conductors in each antenna unit are of dissimilar diameters. 